Needle Cell Trench MOSFET

ABSTRACT

A power semiconductor die has a semiconductor body coupled to first and second load terminals, and at least one power cell. In a horizontal cross-section of the at least one power cell, a contact has a contact region which horizontally overlaps with a field plate electrode and horizontally protrudes from the field plate trench, and a recess region does not horizontally overlap with the contact region and extends into a horizontal circumference of the field plate trench.

TECHNICAL FIELD

This specification is directed to embodiments of a power semiconductordie and to embodiments of a method of processing a power semiconductordie. In particular, this specification is directed embodiments of aMOSFET having a field plate electrode included in a needle cell trenchand to corresponding embodiments of a processing method.

BACKGROUND

Many functions of modern devices in automotive, consumer and industrialapplications, such as converting electrical energy and driving anelectric motor or an electric machine, rely on power semiconductordevices.

For example, Insulated Gate Bipolar Transistors (IGBTs), Metal OxideSemiconductor Field Effect Transistors (MOSFETs) and diodes, to name afew, have been used for various applications including, but not limitedto switches in power supplies and power converters.

A power semiconductor device usually comprises a power semiconductor dieconfigured to conduct a load current along a load current path betweentwo load terminals of the device. A first load terminal, e.g., a sourceterminal, may be arranged at a front side of the die, and a second loadterminal, e.g., a drain terminal, may be arranged at a back side of thedie. The die may be included within a package of the power semiconductordevice, wherein such package may provide for electrical connections tothe load terminals.

Further, the load current path may be controlled by means of a controlelectrode, often referred to as gate electrode. For example, uponreceiving a corresponding control signal from, e.g., a driver unit, thecontrol electrode may set the power semiconductor die in one of aconducting state and a blocking state.

For conducting the load current, the power semiconductor die may haveone or more power cells which may be arranged in a so-called activeregion of the power semiconductor device. For example, within the activeregion, the one or more power cells are electrically connected to thefront side load terminal.

The active region may be configured with a stripe pattern, according towhich the power cells extend in a stripe like manner through the entireactive region or substantial parts thereof, or the active region may beconfigured with a cellular/grid pattern, according to which the powercells exhibit a columnar design (also referred to as “needle design”)and are distributed within the active region.

The present specification is directed to the latter case, i.e., to a diewith an active region where the cells are arranged in accordance with agrid pattern. For example, in accordance with such grid pattern, gatetrenches may form grid openings (e.g., grid meshes), and each gridopening may spatially confine one power cell. For example, the gatetrenches extend longitudinally, in the active region, along linear linesthat perpendicularly cross each other. Further, in each grid opening,there may be arranged a columnar (e.g. needle) trench housing a columnar(e.g. needle) trench electrode connected to a different electricalpotential as compared to gate electrodes in the gate trenches.

The power semiconductor die is laterally confined by a die edge, andbetween the die edge and the active region, there is usually arranged aso-called edge termination region. In terms of power semiconductor dies,such edge termination region is also referred to as a “high voltagetermination structure”, and it may serve the purpose of supporting thevoltage handling capability of the power semiconductor die, e.g., byinfluencing the course of the electric field within the semiconductordie, e.g., so as to ensure reliable blocking capability of the powersemiconductor die.

A reliable blocking capability is desirable. To this end, a respectivefield plate electrode may be arranged in one or more of the power cells.

On the other hand, a high density of power cells within the activeregion may be desirable in terms of handling high load currents at lowconduction losses.

Further, it may be desirable to contact each field plate electrode so asto connect them to one of the load terminals, e.g., to the sourceterminal of a MOSFET.

SUMMARY

In accordance with some embodiments described herein, it is proposed, atleast for one of the power cells of a needle trench MOSFET, to includethe field plate electrode in a columnar field plate trench. A contactcan be provided that established an electrical connection between, onthe one side, the source terminal of the MOSFET and, on the other side,each of the semiconductor channel zone, the semiconductor source zoneand the field plate electrode.

It is proposed to provide a contact with a contact structure withconducting contact region and an insulating recess region that jointlydefine a structured horizontal layout of the contact, e.g., according towhich the contact region exhibits a cross arrangement. For example, acentral portion of the cross arrangement contacts the field plateelectrode, whereas distal (outer) portions of the cross arrangementcontact both the semiconductor channel region and the semiconductorsource region.

For example, the central portion of the contact region overlapshorizontally entirely with the field plate electrode. Further, thecontact region may extend radially from the central portion so as toestablish contact with both the semiconductor channel zone, thesemiconductor source zone. For example, the contact region is arrangedradial-symmetrically with the field plate electrode.

The recess region may form a non-contact region. For example, the recessregion horizontally overlaps with both the source zone and the fieldinsulator, i.e., it may extend into the horizontal circumference of thefield plate trench.

For example, the recess region may form, at least partially, a supportstructure increasing stability of the wafer in which the powersemiconductor die is implemented. A further increase of stability of thewafer may be achieved due to the reduced amount of the electricallyconductive material (e.g., tungsten). For example, without the recessregion, an open area (where the contact is to be established) would besuch that a complete fill of the contact requires thicknesses ofelectrically conductive material (e.g., tungsten) of at least half thediameter of the contact, which may lead to wafer bow issues.Additionally, the structured horizontal layout formed by the contactregion and the recess region may be more advantageous in terms ofprocessing and costs.

Another advantage may be that, for example, by focusing the electricallycontact into corner regions of the cell, the cell pitch may be reduced.

In accordance with an embodiment, a power semiconductor die has asemiconductor body coupled to a first load terminal and a second loadterminal of the power semiconductor die and configured to conduct a loadcurrent between the load terminals. At least one power cell of the diehas: as a respective part of the semiconductor body, a section of adrift zone of a first conductivity type, a section of a channel zone ofa second conductivity type and a section of a source zone of the firstconductivity type, wherein the channel zone section is electricallyconnected to the first load terminal and isolates the source zonesection from the drift zone section; a columnar field plate trenchextending into the semiconductor body along the vertical direction, thecolumnar field plate trench including a field plate electrode and afield insulator, the field insulator forming a field plate trenchsidewall of the columnar field plate trench; a control trench structurefor controlling the load current, the control trench structure extendinginto the semiconductor body along the vertical direction and surroundingthe columnar field plate trench, the control trench structure includingat least one control electrode section and a control trench insulator,the control trench insulator forming control trench sidewalls of thecontrol trench structure; a contact configured for establishing anelectrical connection between the first load terminal and each ofchannel zone section, the source zone section and the field plateelectrode, wherein, in a horizontal cross-section of the at least onepower cell: the contact has a contact region horizontally overlappingwith the field plate electrode and horizontally protruding from thefield plate trench; and a recess region horizontally not overlappingwith the contact region, but horizontally overlapping with the sourcezone section and extending into a horizontal circumference of the fieldplate trench.

In accordance with a further embodiment, a method of processing a powersemiconductor die is presented. The method comprises forming asemiconductor body to be coupled to a first load terminal and a secondload terminal of the power semiconductor die and configured to conduct aload current between the load terminals. The method further comprisesforming at least one power cell having: as a respective part of thesemiconductor body, a section of a drift zone of a first conductivitytype, a section of a channel zone of a second conductivity type and asection of a source zone of the first conductivity type, wherein thechannel zone section is electrically connected to the first loadterminal and isolates the source zone section from the drift zonesection; a columnar field plate trench extending into the semiconductorbody along the vertical direction, the columnar field plate trenchincluding a field plate electrode and a field insulator, the fieldinsulator forming a field plate trench sidewall of the columnar fieldplate trench; a control trench structure for controlling the loadcurrent, the control trench structure extending into the semiconductorbody along the vertical direction and surrounding the columnar fieldplate trench, the control trench structure including at least onecontrol electrode section and a control trench insulator, the controltrench insulator forming control trench sidewalls of the control trenchstructure; a contact configured for establishing an electricalconnection between the first load terminal and each of channel zonesection, the source zone section and the field plate electrode, wherein,in a horizontal cross-section of the at least one power cell: thecontact has a contact region horizontally overlapping with the fieldplate electrode and horizontally protruding from the field plate trench;and a recess region horizontally not overlapping with the contactregion, but horizontally overlapping with the source zone section andextending into a horizontal circumference of the field plate trench.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The parts in the figures are not necessarily to scale, instead emphasisbeing placed upon illustrating principles of the invention. Moreover, inthe figures, like reference numerals designate corresponding parts. Inthe drawings:

FIG. 1 schematically and exemplarily illustrates a section of ahorizontal projection of a power semiconductor die in accordance withone or more embodiments;

FIG. 2 schematically and exemplarily illustrates a section of a verticalcross-section of a power semiconductor die in accordance with one ormore embodiments;

FIG. 3 schematically and exemplarily illustrates a section a section ofa vertical cross-section of a power semiconductor die in accordance withone or more embodiments;

FIG. 4 schematically and exemplarily illustrates a section of ahorizontal projection of a contact of a power semiconductor die inaccordance with one or more embodiments; and

FIG. 5 schematically and exemplarily illustrates sections of ahorizontal projection of a contact of a power semiconductor die inaccordance with some embodiments;

FIG. 6 schematically and exemplarily illustrates sections of ahorizontal projection of a contact of a power semiconductor die inaccordance with some embodiments;

FIG. 7 schematically and exemplarily illustrates sections of ahorizontal projection of a contact of a power semiconductor die inaccordance with some embodiments; and

FIG. 8 schematically and exemplarily illustrates aspects of a method ofprocessing a power semiconductor die in accordance with someembodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof and in which are shown byway of illustration specific embodiments in which the invention may bepracticed.

In this regard, directional terminology, such as “top”, “bottom”,“front”, “behind”, “back”, “leading”, “trailing”, “below”, “above” etc.,may be used with reference to the orientation of the figures beingdescribed. Because parts of embodiments can be positioned in a number ofdifferent orientations, the directional terminology is used for purposesof illustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

Reference will now be made in detail to various embodiments, one or moreexamples of which are illustrated in the figures. Each example isprovided by way of explanation, and is not meant as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be used on or in conjunction with other embodiments toyield yet a further embodiment. It is intended that the presentinvention includes such modifications and variations. The examples aredescribed using specific language which should not be construed aslimiting the scope of the appended claims. The drawings are not scaledand are for illustrative purposes only. For clarity, the same elementsor manufacturing steps have been designated by the same references inthe different drawings if not stated otherwise.

The term “horizontal” as used in this specification intends to describean orientation substantially parallel to a horizontal surface of asemiconductor substrate or of a semiconductor structure. This can be forinstance the surface of a semiconductor wafer or a die or a chip. Forexample, both the (first) lateral direction X and the (second) lateraldirection Y mentioned below can be horizontal directions, wherein thefirst lateral direction X and the second lateral direction Y may beperpendicular to each other.

The term “vertical” as used in this specification intends to describe anorientation which is substantially arranged perpendicular to thehorizontal surface, i.e., parallel to the normal direction of thesurface of the semiconductor wafer/chip/die. For example, the extensiondirection Z mentioned below may be an extension direction that isperpendicular to both the first lateral direction X and the secondlateral direction Y.

In the context of the present specification, the terms “in ohmiccontact”, “in electric contact”, “in ohmic connection”, and“electrically connected” intend to describe that there is a low ohmicelectric connection or low ohmic current path between two regions,sections, zones, portions or parts of the device described herein.

Further, in the context of the present specification, the term “incontact” intends to describe that there is a direct physical connectionbetween two elements of the respective semiconductor device; e.g., atransition between two elements being in contact with each other may notinclude a further intermediate element or the like; i.e., said twoelements may be in touch with each other.

In addition, in the context of the present specification, the term“electric insulation” is used, if not stated otherwise, in the contextof its general valid understanding and thus intends to describe that twoor more components are positioned separately from each other and thatthere is no ohmic connection connecting those components. However,components being electrically insulated from each other may neverthelessbe coupled to each other, for example mechanically coupled and/orcapacitively coupled and/or inductively coupled. To give an example, twoelectrodes of a capacitor may be electrically insulated from each otherand, at the same time, mechanically and capacitively coupled to eachother, e.g., by means of an insulation, e.g., a dielectric.

In this specification, n-doped is referred to as “first conductivitytype”, while p-doped is referred to as “second conductivity type”.Alternatively, opposite doping relations can be employed so that thefirst conductivity type can be p-doped and the second conductivity typecan be n-doped.

Specific embodiments described in this specification pertain to, withoutbeing limited thereto, a power semiconductor die, e.g., a powersemiconductor die that may be used within a power converter or a powersupply. For example, the power semiconductor die described herein isconfigured to be employed within power rectifier or within a powerinverter, e.g., within a synchronous power rectifier or power inverter.For example, such rectifier/inverter is used as a part of a motor drive.Thus, in an embodiment, the power semiconductor die described herein canbe configured to carry a part of a current that is to be fed to a loadand/or, respectively, that is provided by a power source.

Accordingly, the term “power semiconductor die” as used in thisspecification intends to describe a single die with high voltageblocking and/or high current-carrying capabilities. In other words, suchpower semiconductor die is intended for high current, typically in theAmpere range, e.g., up to 5 or 300 Amperes, and/or voltages typicallyabove 15 V, more typically up to 400 V, and above, e.g., up to at least500 V or more than 500 V, e.g. at least 600 V. Further, the powersemiconductor die described herein can be configured for high switchingfrequencies, e.g., for a switching frequency of at least 100 kHz and upto 2 MHz.

For example, the power semiconductor die described below may be a diethat is configured to be employed as a power component in a low-,medium- and/or high voltage application.

Further, the term “power semiconductor die” as used in thisspecification is not directed to logic semiconductor devices that areused for, e.g., storing data, computing data and/or other types ofsemiconductor-based data processing.

For example, the die may comprise one or more active power cells, suchas a monolithically integrated transistor cell, e.g., a monolithicallyintegrated MOSFET cell and/or derivatives thereof. A plurality of suchpower cells may be integrated in the die.

In accordance with the embodiments described herein, the powersemiconductor die includes power cells which are of the columnar/needletype. For example, the power cells are not of the stripe type. Thecolumnar/needle type cells can each comprise at least one columnartrench, e.g., a columnar field plate trench. For example, in accordancewith such columnar/needle configuration, the total lateral extensions ofeach columnar/needle power cell along each of the first lateraldirection X and the second lateral direction Y amount to only a fractionof the total lateral extensions along the first lateral direction X andthe second lateral direction Y of the power semiconductor die. Forexample, the total lateral extension of a respective columnar/needlecell amounts to less than 1%, or to even less than 0.05% of the totalextension of the power semiconductor die along one of the first lateraldirection X and the second lateral direction Y. For example, a die witha side length of approx. 4 mm along the first lateral direction X and atypical cell pitch of approx. 2 μm leads to total lateral extension of arespective columnar/needle cell of approx. 2/4000=0.05% of the totalextension of the die along the first lateral direction X. Further, eachcolumnar/needle cell can exhibit, in parallel to the XY-plane, arectangular, e.g., a quadratic horizontal cross-section, e.g., arectangular horizontal cross-section with rounded corners, or anelliptical horizontal cross-section, or a circular horizontalcross-section, or a polygonal, e.g., an octagonal or a hexagonalhorizontal cross-section. The course of such cross-sections may bedefined by means of grid pattern of control trench structure, as willbecome more apparent from the description of the drawings.

In an embodiment, each columnar/needle power cell has a maximum lateralextension and a maximum vertical extension, wherein the maximum lateralextension is smaller than ½, ⅓, ¼ or ⅕ of the maximum vertical extensionor even yet smaller than ⅙ of the maximum vertical extension. Forexample, the maximum vertical extension is defined by the totalextension of the columnar field plate trench (as mentioned below) alongthe vertical direction of the respective columnar/needle power cell.

In the following, the term power cell refers to a columnar/needle powercell, e.g., as exemplary defined above.

As used herein, the term “needle” includes but is not limited to designsaccording to which a trench bottom is tapered (like a needle); rather,the term “needle” also includes those designs according to which thetrench bottom is substantially flat, e.g., extends horizontally.

FIG. 1 schematically and exemplarily illustrates a section of ahorizontal projection of a power semiconductor die 100 in accordancewith one or more embodiments. FIGS. 2 and 3 both schematically andexemplarily illustrate a respective section of a vertical cross-sectionof the power semiconductor die 100 in accordance with some embodiments.In the following, it will be referred to FIGS. 1-3.

The power semiconductor die has a semiconductor body 190 coupled to afirst load terminal 101 and a second load terminal 102 of the powersemiconductor die 100. The die 100 can be MOSFET and, hence, the firstload terminal 101 may be a source (emitter) terminal and the second loadterminal 102 may be a drain (collector) terminal.

The first load terminal 101 may be arranged at a front side of the die100, and the second load terminal 102 may be arranged at a backside ofthe die 100. The front side of the die 100 may be in proximity to anupper surface 1900 of the semiconductor body 190. For example, the firstload terminal 101 includes a front side metallization, and the secondload terminal 102 includes a backside metallization.

The semiconductor body 190 is configured to conduct a load currentbetween the load terminals 101, 102, e.g., a load current of at least 5A, 10 A, of at least 50 A or of even more than 100 A.

The die 100 includes a control trench structure 110 for controlling theload current. The control trench structure 110 extends into thesemiconductor body 190 along the vertical direction Z and is arranged inaccordance with a horizontal grid pattern having a plurality of gridopenings 116, e.g., as illustrated in FIG. 1.

The control trench structure 110 may comprise a control electrode 111that is electrically insulated from the semiconductor body 190, e.g., bymeans of a control trench insulator 112. The control electrode 111 maybe coupled to an output of a driver unit (not illustrated) and,responsive to a control signal received via the output, set the die 100in one of the conducting state, during which the load current isconducted between the load terminals 101 and 102, and the blockingstate, during which a positive forward voltage is blocked between theload terminals 101 and 102 and flow of the load current is inhibited,the positive forward voltage being present if the electrical potentialof the second load terminal 102 is greater than the electrical potentialof the first load terminal 101.

For conduction of the load current, the die 100 may comprise a pluralityof power cells 120. For example, these power cells 120 are arrangedwithin an active region 105 of the power semiconductor die 100. A dieedge 107 laterally terminates the die 100, and an edge terminationregion 106 is arranged between the die edge 107 and the active region105. For example, the edge termination region 106 is not configured forconduction of the load current.

The control trench structure 110 extends mainly within the active region105 and, there, into the semiconductor body 190 along the verticaldirection Z, e.g., for a distance of at least 500 nm, at least 600 nm,or at least 700 nm, wherein the extension of the control trenchstructure 110 along the vertical direction Z may, e.g., be chosen independence of the designated maximum blocking voltage of the die 100.For example, the extension of the control trench structure 110 along thevertical direction Z is the distance between the upper surface 1900 anda bottom 115 of the control trench structure 110.

The grid pattern with the plurality of the grid openings 116 definessubregions within the active region 105. For example, each grid opening116 is associated with one of the plurality of power cells 120.

The grid openings 116 are illustrated as exhibiting rectangularhorizontal circumference, wherein it shall be understood that thepresent specification is not limited to such horizontal circumferences;e.g., in another embodiment, the grid openings 116 may exhibit acircular or ellipsoidal circumference or rectangular circumference withrounded corners. However, the grid openings 116 typically exhibit arectangular horizontal circumference. It shall further be understoodthat the grid openings 116 must not necessarily be completely surroundedby the respective part of the grid pattern. For example, depending onthe design of the control trench structure 110, there may be small gaps(not illustrated), for example, at intersection points betweenintersecting stripes of the control trench structure 110.

For example, each grid opening 116 exhibits a maximal horizontalextension (cf. distance P (Pitch) indicated in FIG. 2) of no more than afew micrometers, e.g., of no more than 5 μm or of no more than 2 μm. Forexample, such maximal horizontal extension may be the width of therespective grid opening 116 along the first lateral direction X or thelength along the second lateral direction Y, whichever is greater.

Accordingly, each power cell 120 is, in a horizontal cross-section, atleast partially arranged in a respective one of the plurality of gridopenings 116.

FIG. 2 shows an exemplary configuration of four adjacent grid openings116, each being associated with one power cell 120.

For example, all power cells 120 have the same configuration. In anotherembodiment, the power cells 120 may differ in configuration; e.g., it ispossible that the active region 105 includes power cells of a first typeand power cells of a second type and, optionally, even one or more cellsof a further type, e.g., auxiliary cells or dummy cells. The followingdescription refers to the case where at least the power cells 120 aresubstantially identically configured, wherein, as pointed out, it shouldbe understood that this must not necessarily be the case. Rather, thepower cells 120 may also differ from each other.

Each power cell 120 comprises a drift zone section 191 of the firstconductivity type, a channel zone section 192 of the second conductivitytype and a source zone section 193 of the first conductivity type. Thechannel zone section 193 isolates the source zone section 192 from thedrift zone section 191, wherein the source zone section 192 iselectrically connected to the first load terminal 101. Also, the channelzone section 193 may be electrically connected to the first loadterminal 101.

As illustrated, the first load terminal 101 may extend within asubstantially horizontal layer that is spatially displaced from thesemiconductor body 190 at least by means of a first substantiallyhorizontal insulating layer 1012 and, optionally, a second horizontalinsulating layer 104.

As will be described in greater detail below, for implementing saidelectrical connection between the source zone section 193 and the firstload terminal 101, contacts 170 may be employed. For example, thesecontacts 170 penetrate the first insulation layer 1012 (said penetrationnot being illustrated in FIG. 2) and the second insulation layer 104.For example, in each power cell 120, the source zone section 193 and thechannel zone section 192 are arranged in contact with the respectivecontact 170.

As also illustrated in FIG. 3, the source zone 193 and the channel zone192 may contiguously extend within the semiconductor body 190, e.g.,into each of the power cells 120. Hence, with respect to a respectivepower cell 120, the formulations “source zone section” and “channel zonesection” have been chosen. The same applies to the drift region(section) 191.

A transition between the channel zone 192 and the drift zone 191 forms apn-junction 194. For example, the drift zone 191 forms the major portionof the semiconductor body 190 and extends along the vertical direction Zuntil it interfaces with a doped contact region 198 which iselectrically connected to the second load terminal 102. The dopedcontact region 198 may contiguously extend along the lateral directionsX and Y so as to form the homogeneous semiconductor layer thathorizontally (i.e., along the lateral directions X and Y) overlaps withall power cells 120. For example, the doped contact region 198 comprisesor is a field stop layer of the first conductivity type, e.g., the sameconductivity type as the drift region 190, but having a higher dopantconcentration.

Each power cell 120 further comprises a control section with at leastone control electrode section 111 included in the control trenchstructure 110, as has already been indicated above. The controlelectrode sections 111 are electrically insulated from each of the firstload terminal 101, the second load terminal 102 and the semiconductorbody 190.

Regarding the components control electrode section 111, source zonesection 193, channel zone section 192 and drift zone section 191, theprincipal configuration of each power cell 120 corresponds to thetypical MOSFET configuration, according to which the control electrodesection 111 may induce, upon receiving a corresponding turn-on controlsignal, an inversion channel within the channel zone section 192, and,upon receiving a corresponding turn off control signal, cut-off thisinversion channel. The general operation principle is described inlittle more detail further below; however; it is such known to theskilled person and the embodiments described herein do not deviate fromthis general operation principle.

The control electrode sections 111 of the power cells 120 may be formedby a respective monolithic stripe control electrode, these stripeelectrodes being included in the stripes of the control trench structure110 as illustrated in FIG. 1. Hence, it shall also be understood that aspecific control electrode section 111 may be associated with twoadjacent power cells 120, as illustrated in FIGS. 2 and 3. In otherwords, each power cell 120 may for example be controlled by means offour control electrode sections 111 that surround the source zonesection 193 and the channel zone section 192 of the respective powercell 120.

The control electrode sections 111 may vertically overlap with both thesource zone section 193 and the channel zone section 192. In otherwords, in each power cell 120, the at least one control electrodesection 111 and the source zone section 193 may exhibit a first commonextension range along the vertical direction Z e.g., of 100 nm, and theat least one control electrode section 111 the channel zone section 192may exhibit a second common extension range along the vertical directionZ, e.g., of 50 nm. Further, the at least control electrode section 111may extend as least as deep as said pn-junction 194.

Each power cell 120 may further comprise a columnar field plate trench130 extending into the semiconductor body 190 along the verticaldirection Z and including a field plate electrode 131, e.g.,electrically coupled to the first load terminal 101.

For example; the field plate electrodes 131 are electrically connectedto the first load terminal 101, e.g., such that the electrical potentialof the field plate electrodes 131 is substantially identical to theelectrical potential of the first load terminal 101. For example, toimplement the electrical connection, also said contacts 170 may beemployed that may extend from the first load terminal 101 down to thefield plate trenches 130 so as to contact the field plate electrodes 131and the source zone sections 193. For improving the contact,electrically conductive adhesion promoters 1016 may be used, asillustrated.

Regarding the contacts 170, it shall hence be understood that, asillustrated in FIGS. 2-3, it is possible to electrically connect thefirst load terminal 101 to each of the channel zone section 192, thesource zone section 193 and the field plate electrode 131 by means of arespective joint contact 170. For example, the electrical connection ofeach power cell 120 to the first load terminal 101 can be effected bymeans of a respective single joint contact 170, in accordance with anembodiment.

Hence, the contact 170 can be monolithic.

In contrast to the common name “field plate electrode”, the field plateelectrodes 131 do typically not exhibit the shape of a plate, but ratherof a column/needle, as also illustrated in FIGS. 2 and 3.

In each field plate trench 130, a field insulator 132 may be providedthat insulates the respective field plate electrode 131 from thesemiconductor body 190.

For example, the total vertical extension of each columnar field platetrench 130 amounts to at least twice of the total vertical extension ofthe control trench structure 110; e.g., each columnar field plate trench130 extends at least three times as far along the vertical direction Zas compared to the control trench structure 110, e.g., taking the uppersurface 1900 of the semiconductor body 190 as a reference. For example,the extension of h columnar field plate trench 130 along the verticaldirection Z is the distance between the upper surface 1900 and a bottom135 of the respective columnar field plate trench 130.

As illustrated in FIGS. 2 and 3, the field insulator 132 forms a fieldplate trench sidewall 134 of the columnar field plate trench 130.Analogously, the control trench insulator 112 forms control trenchsidewalls 114 of the control trench structure 110. Further, in eachpower cell 120, the control trench structure 110 may surround thecolumnar field plate trench 130, e.g., as best illustrated in FIG. 2,inner ones of the control trench sidewalls 114 surround the field platetrench sidewall 134. The source zone section 193 can be arranged incontact with both the field plate trench sidewall 134 and the controltrench sidewall 114.

In between the (inner) control trench sidewalls 114 and the field platetrench sidewall 134, there may be arranged each of the source zonesection 193, the channel zone section 192 and the drift zone section 191of the respective power cell 120.

As indicated above, for connecting the power cells 120 to the first loadterminal, at least one of said contacts 170 may be provided for eachpower cell 120. In an embodiment, exactly one contact 170 is providedfor each power cell 120. Said respective exactly one contact 170 can bemonolithic, as indicated above.

Each contact 170 is configured for establishing an electrical connectionbetween the first load terminal 101 and each of the channel zone section192, the source zone section 193 and the field plate electrode 131 ofthe respective power cell 120. For example, each contact 170 isconfigured to form a low ohmic electrical connection between the firstload terminal 101 and each of the channel zone section 192, the sourcezone section 193 and the field plate electrode 131.

Now referring to FIG. 4, which illustrates a horizontal cross-section ofan embodiment of such contact 170, e.g., along or in parallel to lineHH′ as indicated in FIG. 3, in a horizontal cross-section of the atleast one power cell 120:

-   -   the contact 170 has a contact region 171 horizontally        overlapping with the field plate electrode 131 and horizontally        protruding from the field plate trench 130, e.g., so as to make        contact with at least one of the channel zone section 192 and        the source zone section 193; and    -   a recess region 172 horizontally not overlapping with the        contact region 171, but horizontally overlapping with the source        zone section 193 and extending into a horizontal circumference        of the field plate trench 130.

The field plate electrode 131 may entirely horizontally overlap with thecontact region 171, e.g., with a central portion 1713 thereof. Hence, anupper surface of the plate electrode 131 may entirely be covered by thecontact region 171.

With respect to the vertical axis Z1 (e.g., the center of the fieldplate electrode 131), the contact region 171 may extend radially, e.g.,radial-symmetrically, e.g., so as to protrude from the field platetrench 13 and to establish the contact with both channel zone section192 and the source zone section 193. For example, “protruding from thefield plate trench 13” may mean that the contact region 171 extendsbeyond the horizontal circumference of the field plate trench 130.

The horizontal circumference of the field plate trench 13 may be definedby the circumference of the field insulator 132 in said horizontalcross-section. The horizontal circumference of the field plate trench130 may for example be defined by the field plate trench sidewall 134.

The recess region 172 is electrically insulating. Hence, recess region172 and contact region 171 do not horizontally overlap with each otherin the horizontal cross-section. They may be in direct contact with eachother, but are separate components.

Together with the contact region 171, the recess region 172 may hencedefine the horizontal layout of the structure of the contact 170.

The recess region 172 extends within the horizontal circumference of thefield plate trench 130, but does not form a conducting portion betweenthe field plate electrode 131 (or the source zone section 193 or thechannel zone section 192) and the first load terminal 101. For example,the recess region 172, e.g., when being filled with an electricallyinsulating material, can rather act as a support structure for thecontact 170.

The recess region 172 may horizontally overlap with both the source zonesection 193 and the field insulator 132 of the field plate trench 13.

The contact region 171 of the contact 170 can horizontally protrude outof the horizontal circumference of the field plate trench 130 (e.g., soas to contact at least one of the channel zone section 192 and thesource zone section 193) and may also extend within the horizontalcircumference of the field plate trench 130 (e.g., so as to contact thefield plate electrode 131).

The recess region 172 extends within the horizontal circumference of thefield plate trench 130. For example, the contact region 171 and therecess region 172 are arranged complementarily to each other within thehorizontal cross-section; e.g., the regions 171 and 172 do not exhibit acommon horizontal extension range.

For example, the contact region 171 extends within a rectangular basearea 1700 that is defined by an outer envelope course of the contact170. This outer envelope course can be rectangular. For example, therectangular base area 1700 is surrounded by the grid opening 116.Further, the grid opening 116 can have a rectangular circumference, andthe rectangular base area 1700 can be arranged co-parallel within thegrid opening 116. In the illustrated horizontal cross-section, the areabetween the rectangular base area 1700 and the control trench structure110, that is the area between the control trench sidewalls 114 and theouter envelope course of the rectangular base area 1700, can be formedby the source zone section 193 and/or the channel zone section 192.

A minimum distance dl between the control trench sidewall 114 facing toa center (cf. Z1 in FIG. 4) of the of the horizontal circumference ofthe field plate trench 130 and the rectangular base area 1700 can bewithin the range of, e.g., 50 nm to 300 nm, e.g., within 80 nm to 200nm, such as 150 nm. For example, the minimum distance dl can be theminimum lateral extension of the source zone section 193 in said areabetween the control trench sidewalls 114 and the outer envelope courseof the rectangular base area 1700. For example, the minimum distance dldefines said horizontal displacement between the contact and the controltrench sidewalls 114.

The recess region 172 can be filled with (or, respectively, be made of)an electrically insulating material, and the contact region 171 can bemade of an electrically conductive material, and wherein both theinsulating material and the conductive material extend with therectangular base area 1700.

The conductive material may comprise tungsten.

The insulating material may comprise silicon glass (SiO2), e.g., undopedsilicon glass or doped silicon glass. Other possible materials includesilicon nitride and silicon oxynitride.

The contact 170 (which may be identical for each power cell 120) canhave the layout according to the illustrated horizontal cross-section ofa vertical extension of at least 150 nm. For example, both the contactregion 171 and the at least one recess region 172 extend along thevertical direction Z for at least 150 nm, e.g., without changing inhorizontal layout.

Further, as indicated above, the first load terminal 101 may extendwithin the substantially horizontal layer that is spatially displacedfrom the semiconductor body 190 at least by means of a substantiallyhorizontal insulating layer(s) (cf. reference numerals 104, 1012). Thecontact 170 may extend through the insulating layer(s) (cf. referencenumerals 104, 1012). Further, as illustrated, the horizontalcross-section of the contact 170 may include a vertical overlap betweenthe at least one control electrode section 111 (and also the source zonesection 193) and the contact region 171.

With respect to FIGS. 4 to 7, exemplary horizontal layout structures ofthe contact 170 shall be described:

For example, at least 30% of the outer envelope course of the contact170 are defined by the contact region 171, and at least 20% of the outerenvelope course of the contact 170 are defined by the recess region 172.Hence, in an embodiment, the outer envelope course of the contact 170 isnot entirely defined by the contact region 171, but at least partiallyby the recess region 172. For example, the recess region 172 mayinterface with the source zone section 193, as illustrated in FIG. 4.

In an embodiment, at least four separate recess regions 172 extendwithin the horizontal circumference of the field plate trench 130. Forexample, each of the four separate recess regions 172 is arranged at onerespective side of the four sides of the rectangular base area 1700.

For example, the contact region 171 comprises two bar members 1711, 1712arranged in accordance with a cross pattern. Additionally oralternatively, the contact region 171 may comprise five block members,wherein the four recess regions 172 and the five block members can bearranged in accordance with a check pattern (cf. FIG. 5, variant (c)).

For example, by horizontally protruding from the field plate trench 130(e.g., out of the horizontal circumference thereof), distal portions ofthe bar members 1711, 1712 are configured for contacting both thechannel zone section 192 and the source zone section 193. For example,the distal portions of the bar members 1711, 1712 define, at leastpartially, the outer envelope course of the base area 1700.

It shall be understood that, depending on the arrangement of the channelzone section 192 and the source zone section 193, the contact betweenthe distal portions of the bar members 1711, 1712 with the channel zonesection 192 and the source zone section 193 can be established at thesame of at a different vertical level (cf. vertical cross-section inFIG. 2).

A central portion 1713 where the bar members 1711, 1712 intersect witheach other can be configured for contacting the field plate electrode131.

In an embodiment, the bar members 1711, 1712 are arranged in parallelwith two straights (cf. line VV′ in FIG. 4) perpendicularly intersectingthe center (Z1) of the horizontal circumference of the field platetrench 130, e.g., with diagonals of the rectangular base area 1700. Thebar members 1711, 1712 can horizontally from the field plate trench 130(e.g., protrude out of the horizontal circumference of the field platetrench 130), e.g., by extending beyond the field insulator 132 so as tocontact at least one of the channel zone section 192 and the source zonesection 193.

The central portion 1713, e.g., formed by the intersection region of thebar members 1711, 1712, contacts the field plate electrode 131 (cf.dotted line). As indicated above, the field plate electrode 131 canentirely overlap horizontally with the contact region 171, e.g., withsaid central portion 1713. For example, the central portion 1713 coversentirely an upper surface of the field plate electrode 131.

The four recess regions 172 may partially separate the two bar members1711, 1712 from each other, such that the cross-pattern is established,as illustrated in FIG. 4. In other words, the distal portions of the barmembers 1711, 1712 can be spatially separated from each other by meansof the four recess regions 172.

Simultaneously, at least one, more than one or all four recess regions172 horizontally overlap with (a) the source zone section 193 and,optionally, also with the channel zone section 192 and with (b) thehorizontal circumference of the field plate trench 130, e.g., only withthe field insulator 132, but not with the field plate electrode 131.

The contact region 171 and the recess region 172 may jointly define,with respect to axis Z1, a radial-symmetrical layout structure of thecontact 170.

For example, as illustrated, the central portion 1713 entirely overlapshorizontally with the field plate electrode 131. In other variants, alsothe recess region 172 may overlap horizontally with the field plateelectrode 131.

Many variations and modifications of the cross pattern as illustrated inFIG. 4 are possible:

For example, referring to FIG. 5 variant (a), the bar members 1711, 1712may be arranged perpendicular to each other within the horizontal crosssection, defining an intersection angle of 90°.

Referring to FIG. 5 variant (b), at least one of the bar members 1711,1712 or both bar members 1711, 1712 may increase in width when extendingfrom the central portion 1713 to one (or both) of its distal portions.This may yield a decreased intersection angle of less than 90°, e.g.,less than 60°, and, e.g., a greater area of the contact interface withthe source zone section 193. In another embodiment (not illustrated), atleast one of the bar members 1711, 1712 decreases in width whenextending from the central portion to one of its distal portions; thismay yield an increased intersection angle of more than 90° e.g., greaterthan 110°.

Another variant is illustrated in FIG. 5 (c), according to which the twobar members 1711, 1712 are essentially formed by four outer contactblocks that are interlinked with each other by means of the centralportion 1713, e.g., also in the form of a block. This layout structuremay yield said check pattern, e.g., with the four recess regions 172being arranged along the outer rectangular envelope course of the basearea 1700 and adjacent to both the central portion 1713 and respectivetwo of the four blocks formed by the bar members 1711, 1712. Forexample, the five blocks of the contact area 171 and the four blocks ofthe recess area 172 may each exhibit the substantially same size.

In FIG. 6, two further variants (a) and (b) are illustrated. Variant (a)corresponds to FIG. 4, in so far, it is referred to the above. However,in FIG. 6, the field plate electrode 131 is not illustrated. Whereas theright section of variant (a) shows the layout according to which acorresponding processing method can be carried out (e.g., a standardlayout according to a lithographic mask), the left section illustratesthat after processing, the layout might be slightly blurred; e.g., theintersection angle of 90° is not strictly maintained; but results in arounded corner, as illustrated in the left section.

Variant (b) of FIG. 6 can be considered as a combination of the variant(a) of FIG. 6 (i.e., variant of FIG. 4) and the variant of FIG. 5 (c),e.g., a combination of cross pattern and a check pattern. Again, asillustrated in the right section of variant (b) in FIG. 6, such strictlayout might be slightly blurred after carrying out the correspondingprocessing steps. Yet, with the layout according FIG. 6 (b), leftsection, an eventually desired cross-pattern of the contact 170 (cf.right section of FIG. 6 (b) can be more appropriately achieved ascompared to the variant according to FIG. 6 (a).

Further exemplary layout structures of the contact 170 will be explainedwith respect to FIG. 7.

In accordance with one or more embodiments described herein; the contact170 exhibits, within said horizontal cross-section, no more than onehorizontal axis of symmetry HS.

For example, referring to variant (a) of FIG. 7, the horizontal layoutcan have an L-structure, wherein a single recess region 172 forms asymmetrical L-shaped recess, e.g., within the rectangular base area1700. For example, the single horizontal axis of symmetry HS extendsdiagonally within the rectangular base area 1700. Further, thesymmetrical L-shaped recess formed by the single recess region 172 canbe entirely surrounded by the contact region 171; i.e., in thisembodiment, the outer envelope course of the rectangular base area 1700is entirely defined by the contact region 171.

Referring to variant (b) of FIG. 7, the horizontal layout can have anI-structure, wherein a single recess region 172 forms a symmetricalI-shaped recess; e.g., within the rectangular base area 1700. Forexample, the single horizontal axis of symmetry HS extends in parallelwith one of the sides of the rectangular base area 1700. Further; thesymmetrical I-shaped recess formed by the single recess region 172 canbe entirely surrounded by the contact region 171; i.e., also in thisembodiment, the outer envelope course of the rectangular base area 1700is entirely defined by the contact region 171.

Referring to variant (c) of FIG. 7, the horizontal layout can have adouble I-structure, wherein a two recess regions 172 form twosymmetrically arranged I-shaped recesses, e.g., within the rectangularbase area 1700. For example, the single horizontal axis of symmetry HSextends in parallel with one of the sides of the rectangular base area1700. Further, the I-shaped recesses formed by the two recess region 172can be partially surrounded by the contact region 171; i.e., in thisembodiment, the outer envelope course of the rectangular base area 1700is not entirely defined by the contact region 171, but also by one ofthe two recess regions 172. For example, the two recess regions 172 arenot centrally arranged within the rectangular base area 1700 such thatthe contact 170 indeed exhibits only the single horizontal axis ofsymmetry HS.

Another possibility is shown in variant (d) of FIG. 7, according towhich the horizontal layout can have a T-structure, wherein a singlerecess region 172 forms the single T-shaped recess, e.g., within therectangular base area 1700. For example, the single horizontal axis ofsymmetry HS extends in parallel with one of the sides of the rectangularbase area 1700. Further, the T-shaped recess formed by the single recessregion 172 can be entirely surrounded by the contact region 171; i.e.,in this embodiment, the outer envelope course of the rectangular basearea 1700 is again entirely defined by the contact region 171.

Variant (e) is a slight modification of variant (a) of FIG. 7; inaccordance with this embodiment, the single recess region 172 forms anon-symmetrical L-shaped recess, e.g.; within the rectangular base area1700. Hence, the contact 170 does not exhibit any horizontal axis ofsymmetry HS.

Referring to all variants (a) to (e) of FIG. 7, as illustrated inrespective upper sections of FIG. 7, the recess region(s) 171 mayhorizontally overlap with the both the field plate electrode 131 and thefield insulator 132. The contact region 171 horizontally overlaps withboth the field plate electrode 131 and the source zone section 193.

Herein presented are also embodiments of a method of processing a powersemiconductor die. For example, the method comprises forming asemiconductor body to be coupled to a first load terminal and a secondload terminal of the power semiconductor die and configured to conduct aload current between the load terminals. The method further comprisesforming at least one power cell having: as a respective part of thesemiconductor body, a section of a drift zone of a first conductivitytype, a section of a channel zone of a second conductivity type and asection of a source zone of the first conductivity type, wherein thechannel zone section is electrically connected to the first loadterminal and isolates the source zone section from the drift zonesection; a columnar field plate trench extending into the semiconductorbody along the vertical direction, the columnar field plate trenchincluding a field plate electrode and a field insulator, the fieldinsulator forming a field plate trench sidewall of the columnar fieldplate trench; a control trench structure for controlling the loadcurrent, the control trench structure extending into the semiconductorbody along the vertical direction and surrounding the columnar fieldplate trench, the control trench structure including at least onecontrol electrode section and a control trench insulator, the controltrench insulator forming control trench sidewalls of the control trenchstructure; a contact configured for establishing an electricalconnection between the first load terminal and each of channel zonesection, the source zone section and the field plate electrode, wherein,in a horizontal cross-section of the at least one power cell: thecontact has a contact region horizontally overlapping with the fieldplate electrode and horizontally protruding from the field plate trench:and a recess region horizontally not overlapping with the contactregion, but horizontally overlapping with the source zone section andextending into a horizontal circumference of the field plate trench.

Embodiments of the method described above may correspond to theembodiments of the power semiconductor die 100 that have been describedwith respect to FIGS. 1 to 7. Hence, regarding exemplary embodiments ofthe methods, it is fully referred to the above.

In particular, it shall be understood that the sequence of executing theindividual method steps may be appropriately chosen by the skilledperson.

Aspects of an exemplary embodiment of the method will now be explainedwith respect to FIG. 8, which schematically illustrates differentprocessing stages based (i) to (iv) on corresponding states of theprocessed power semiconductor die 100, indicated by both a respectivesection of a horizontal projection (upper part of FIG. 8) and arespective section of a vertical cross-section (lower part of FIG. 8).

For example, at stage (i), the columnar field plate trenches 130 areformed in the active region 105. Forming the columnar field platetrenches 130 can be carried out in typical manner known to the skilledperson.

At stage (ii), the control trench structure 110 is formed. Also formingthe control trench structure 110 can be carried out in typical mannerknown to the skilled person. In contrast to the schematic illustration,the control structure 110 can be formed within the entire cell fieldwhere the columnar field plate trenches 130 have been formed, not onlyin the illustrated central portion.

Stage (iii) shows the die 100 after the source zone 193 and the channelzone 192 have been formed in the semiconductor body 190 and after theinsulating layer 104 has been provided at the upper surface 1900 (notshowing the other insulating layer 1012).

Thereafter, contact recesses 179 may be formed (cf. stage (iv)) thatexpose, within each designated power cell 120 each of the channel zonesection 192, the source zone section 193 and the field plate electrode131. This may include a masked etching processing step. After theetching processing step, a further implantation processing step and/oran annealing processing step may be carried out.

Subsequent (non-illustrated) stages relate to forming the contacts 170within the contact recesses 179. For example, the contact recesses 179are formed in accordance with the designated layout structure of thecontact 170.

For example, in case of the cross-pattern, a correspondingly structuredmask having cross-patterns can be used for forming the contact recesses179 in layer 104. Providing such mask may be followed by aphotolithographic processing step, an anisotropic oxide etch processingstep, an anisotropic Si etch processing step. For example, thereafter, abody implantation processing step may be carried out for improving theelectrical contact to the channel zone sections 192. For example,thereafter, the recesses 179 are filled with a conductive material(e.g., including one or more of the following materials: titanium (Ti),titanium-nitrogen (TiN) and tungsten (W).) for forming the contactregions 171.

In more general terms, in the above, an embodiment of a semiconductordie 100 has been presented that may include a semiconductor substrate(e.g., semiconductor body 190) with gate trenches (e.g., control trenchstructure 110) extending into the front surface (e.g., upper surface1900) of the semiconductor substrate. The semiconductor substrate cancomprise any type of semiconductor material such as a single elementsemiconductor (e.g. Si, Ge, etc.), silicon-on-insulator, a binarysemiconductor (e.g. SiC, GaN, GaAs, etc.), a ternary semiconductor, etc.with or without epitaxial layer(s). A gate electrode (e.g., controlelectrode sections 111) and a gate dielectric (e.g., trench insulator112) are disposed in each gate trench, the gate dielectric separatingthe corresponding gate electrode from the semiconductor substrate. Afield plate (e.g., field plate electrode 131) can be disposed incolumnar field plate trenches 130, each field plate being separated fromthe semiconductor substrate and the corresponding gate electrode by afield dielectric (e.g., field insulator 132) that is, e.g., thicker thanthe gate dielectric. Alternatively or additionally, field plates can bedisposed in trenches that house also the gate electrodes.

A first (source/emitter) region (e.g. source zone 193) having a firstconductivity type (e.g. n-type in the case of an n-channel device, orp-type in the case of a p-channel device) is formed in the semiconductorsubstrate at the front surface and adjacent each gate trench. A second(body) region (e.g. channel zone 192) having a second conductivity type(e.g. p-type in the case of an n-channel device, or n-type in the caseof a p-channel device) is formed in the semiconductor substrate belowthe source/emitter region and adjacent each gate trench. A third (drift)region (e.g. drift zone 191) having the first conductivity type isformed in the semiconductor substrate, e.g. as part of an epitaxiallayer, below the body region and adjacent each gate trench. Adrain/collector region (cf. doped contact region 198) of the firstconductivity type is formed at the back surface of the semiconductorsubstrate opposite the front surface, and is doped more heavily than thedrift region. Further, in particular in case another material than Si isused, one could also imagine a pnp instead of an npn MOSFET.

The semiconductor die illustrated can be a vertical power MOSFET whichhas a channel zone that extends in the vertical direction Z along gatedielectric (cf. 112) in the body region (cf. 192). By applying asufficient gate voltage to the gate electrodes, minority carriers(electrons in the case of a p-type body region, or holes in the case ofan n-type body region) collect along the gate dielectric in the channelregion and an electrically conductive path is completed between thesource/emitter region and the drain/collector region via the drift andchannel regions.

In the above, embodiments pertaining to power semiconductor dies andcorresponding processing methods were explained. For example, thesesemiconductor dies are based on silicon (Si). Accordingly, amonocrystalline semiconductor region or layer or section can be amonocrystalline Si-region or Si-layer. In other embodiments,polycrystalline or amorphous silicon may be employed.

It should, however, be understood that the semiconductor die can be madeof any semiconductor material suitable for manufacturing a semiconductordie. Examples of such materials include, without being limited thereto,elementary semiconductor materials such as silicon (Si) or germanium(Ge), group IV compound semiconductor materials such as silicon carbide(SiC) or silicon germanium (SiGe), binary, ternary or quaternary III-Vsemiconductor materials such as gallium nitride (GaN), gallium arsenide(GaAs), gallium phosphide (GaP), indium phosphide (InP), indium galliumphosphide (InGaPa), aluminum gallium nitride (AlGaN), aluminum indiumnitride (AIInN), indium gallium nitride (InGaN), aluminum gallium indiumnitride (AlGaInN) or indium gallium arsenide phosphide (InGaAsP), andbinary or ternary II-VI semiconductor materials such as cadmiumtelluride (CdTe) and mercury cadmium telluride (HgCdTe) to name few. Theaforementioned semiconductor materials are also referred to as“homojunction semiconductor materials”. When combining two differentsemiconductor materials a heterojunction semiconductor material isformed. Examples of heterojunction semiconductor materials include,without being limited thereto, aluminum gallium nitride (AlGaN)-aluminumgallium indium nitride (AlGaInN), indium gallium nitride(InGaN)-aluminum gallium indium nitride (AlGaInN), indium galliumnitride (InGaN)-gallium nitride (GaN), aluminum gallium nitride(AlGaN)-gallium nitride (GaN), indium gallium nitride (InGaN)-aluminumgallium nitride (AlGaN), silicon-silicon carbide (SixC1-x) andsilicon-SiGe heterojunction semiconductor materials. For powersemiconductor devices applications currently mainly Si, SiC, GaAs andGaN materials are used.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the respective device inaddition to different orientations than those depicted in the figures.Further, terms such as “first”, “second”, and the like, are also used todescribe various elements, regions, sections, etc. and are also notintended to be limiting. Like terms refer to like elements throughoutthe description.

As used herein, the terms “having”, “containing”, “including”,“comprising”, “exhibiting” and the like are open ended terms thatindicate the presence of stated elements or features, but do notpreclude additional elements or features.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

1. A power semiconductor die having a semiconductor body coupled to afirst load terminal and a second load terminal of the powersemiconductor die and configured to conduct a load current between thefirst and second load terminals, the power semiconductor die comprisingat least one power cell having: as a respective part of thesemiconductor body, a section of a drift zone of a first conductivitytype, a section of a channel zone of a second conductivity type and asection of a source zone of the first conductivity type, the channelzone section being electrically connected to the first load terminal andisolating the source zone section from the drift zone section; acolumnar field plate trench extending into the semiconductor body alonga vertical direction, the columnar field plate trench including a fieldplate electrode and a field insulator, the field insulator forming afield plate trench sidewall of the columnar field plate trench; acontrol trench structure configured to control the load current, thecontrol trench structure extending into the semiconductor body along thevertical direction and surrounding the columnar field plate trench, thecontrol trench structure including at least one control electrodesection and a control trench insulator, the control trench insulatorforming control trench sidewalls of the control trench structure; and acontact configured to establish an electrical connection between thefirst load terminal and each of the channel zone section, the sourcezone section and the field plate electrode, wherein in a horizontalcross-section of the at least one power cell: the contact has a contactregion horizontally overlapping with the field plate electrode andhorizontally protruding from the field plate trench; and a recess regionnot horizontally overlapping with the contact region and extending intoa horizontal circumference of the field plate trench.
 2. The powersemiconductor die of claim 1, wherein the recess region horizontallyoverlaps with the source zone section.
 3. The power semiconductor die ofclaim 1, wherein the recess region is electrically insulating, andwherein the contact region is electrically conductive.
 4. The powersemiconductor die of claim 1, wherein at least four separate recessregions extend within the horizontal circumference of the field platetrench, and wherein the contact region comprises two bar membersarranged in a cross pattern.
 5. The power semiconductor die of claim 4,wherein distal portions of the two bar members are configured to contactboth the channel zone section and the source zone section, and wherein acentral portion where the two bar members intersect with each other isconfigured to contact the field plate electrode.
 6. The powersemiconductor die of claim 5, wherein at least one of the two barmembers increases in width when extending from the central portion to adistal portion of the bar member.
 7. The power semiconductor die ofclaim 5, wherein at least one of the two bar members decreases in widthwhen extending from the central portion to a distal portion of the barmember.
 8. The power semiconductor die of claim 4, wherein distalportions of the two bar members are spatially separated from each otherby the four recess regions.
 9. The power semiconductor die of claim 4,wherein the two bar members are arranged in parallel with two straightsperpendicularly intersecting a center of the horizontal circumference ofthe field plate trench.
 10. The power semiconductor die of claim 1,wherein four separate recess regions extend within the horizontalcircumference of the field plate trench, and wherein the contact regioncomprises five block members, and wherein the four recess regions andthe five block members are arranged in a check pattern.
 11. The powersemiconductor die of claim 1, wherein the contact region isradial-symmetrical with respect to a vertical axis intersecting a centerof the field plate electrode.
 12. The power semiconductor die of claim1, wherein the field plate electrode overlaps entirely with the contactregion.
 13. The power semiconductor die of claim 1, wherein within thehorizontal circumference of the field plate trench, the recess regionoverlaps horizontally exclusively with the field insulator but not withthe field plate electrode.
 14. The power semiconductor die of claim 1,wherein the control trench structure is arranged in a horizontal gridpattern having a plurality of grid openings, and wherein the at leastone power cell is at least partially arranged within one of the gridopenings.
 15. The power semiconductor die of claim 14, wherein each gridopening has a maximal horizontal extension of no more than 5 μm.
 16. Thepower semiconductor die of claim 1, wherein both the contact region andthe recess region extend along the vertical direction for at least 150nm.
 17. The power semiconductor die of claim 1, wherein the first loadterminal extends within a substantially horizontal layer that isspatially displaced from the semiconductor body at least by asubstantially horizontal insulating layer, and wherein the contactextends through the insulating layer.
 18. The power semiconductor die ofclaim 1, wherein the horizontal cross-section includes a verticaloverlap between the at least one control electrode section and thecontact region.
 19. The power semiconductor die of claim 1, wherein thecontact is electrically connected to the first load terminal.
 20. Thepower semiconductor die of claim 1, wherein the contact has, within thehorizontal cross-section, no more than one horizontal axis of symmetry.21. A method of processing a power semiconductor die, the methodcomprising: providing a semiconductor body to be coupled to a first loadterminal and a second load terminal of the power semiconductor die andconfigured to conduct a load current between the load terminals; andforming at least one power cell having: as a respective part of thesemiconductor body, a section of a drift zone of a first conductivitytype, a section of a channel zone of a second conductivity type and asection of a source zone of the first conductivity type, the channelzone section being electrically connected to the first load terminal andisolating the source zone section from the drift zone section; acolumnar field plate trench extending into the semiconductor body alongthe vertical direction, the columnar field plate trench including afield plate electrode and a field insulator, the field insulator forminga field plate trench sidewall of the columnar field plate trench; acontrol trench structure configured to control the load current, thecontrol trench structure extending into the semiconductor body along thevertical direction and surrounding the columnar field plate trench, thecontrol trench structure including at least one control electrodesection and a control trench insulator, the control trench insulatorforming control trench sidewalls of the control trench structure: acontact configured to establish an electrical connection between thefirst load terminal and each of the channel zone section, the sourcezone section and the field plate electrode, wherein in a horizontalcross-section of the at least one power cell: the contact has a contactregion horizontally overlapping with the field plate electrode andhorizontally protruding from the field plate trench; and a recess regionhorizontally not overlapping with the contact region and extending intoa horizontal circumference of the field plate trench.
 22. The method ofclaim 21, wherein the recess region horizontally overlaps with thesource zone section.